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The National Gas Engine Co., Ltd., of Ashton-under-Lyne, took a leading position in the development of the vertical type of this class, and in 1910 erected a special factory for their exclusive manufacture.

An illustration of a 1,500 B.H.P. " National " vertical gas engine direct-coupled to an alternating current generator is given in fig. 4, while fig. 5 shows a transverse section through one of the six pairs of cylinders. It will be seen that this 1,500 B.H.P. engine com- prises twelve cylinders arranged in six vertical tandem single-acting pairs AA and BB respectively (fig. 5) ; the pistons EE are rigidly connected together by a stout piston rod, and from the lower piston the six-throw crankshaft D is driven through a connecting-rod CC. The lower part of the upper cylinder AA is closed, and in this air is compressed during the downward stroke of the pistons thus " soften-
 * ng " the running. The engine works on the four-stroke cycle, and

he inlet and exhaust valves and gas, air, and exhaust passages are jlearly indicated. These engines work on coal gas, Producer gas, coke oven gas or blast furnace gas, and no explosive mixture exists outside the engine itself. The cylinders are well water-jacketed, but the pistons, though not water-cooled, are so designed as to facilitate the conduction of the heat away from their crowns to the surrounding cylinder walls.

FIG. 5.

Engines of this type are built in a series ranging from a ^.-cylinder two-crank design of 300 B.H.P. running at 300 revs, per minute to a 12-cylihder six-crank design of 1,500 B.H.P., 200 revs, per minute.

Many fairly large plants had by 1921 been installed, among which may be mentioned one of n,5ooH.P. at Palmer's Ship- building Co., Ltd., Jarrow; one of 11,000 H.P. at the Government Factory, Lanquith; one of 10,500 H.P. at the Partington Steel Co.'s Works, Irlam, near Manchester; and one of 4,500 H.P. for the Midland Coal & Iron Co., Ltd.

As a typical example of the horizontal type of multi-cylindered single-acting large gas engine, the design adopted by the Premier Gas Engine Co., Ltd., of Sandiacre, Notts., is taken. An impor- tant installation of this type is that of the Hoffmann Mfg. Co., Ltd., at Chelmsford, which commenced operations in March igig. 1

This installation comprises six 500 B.H.P. four-cylinder four- crank horizontal Premier engines running at 190 revs, per minute, each direct-coupled to a 360 K.W.-generator ; thus here 3,000 H.P. is produced from 24 cylinders. Gas is supplied by a Lynn pressure producer plant with ammonia recovery. An examination of the results of six months' working in ordinary service showed that the overall thermal efficiency of this plant, i.e. the ratio of heat of

' For details see Patchell, Journ. Inst. of Elec. Engrs., June 1920.

electrical energy to heat of coal supplied, had the very high value of 199, *'.. 19-9%.

Group 2. Medium-powered' Gas Engines. Included in this group are the very numerous engines principally of the single- cylindered four-stroke horizontal single-acting- type using coal gas or Suction Producer gas as fuel, and employed for a great variety of purposes by the smaller class of power consumers. In H.P. they range from 2 or 3 up to (two-cylindered) designs of about 300. Messrs. Crossley Bros., Ltd., of Manchester, pro- duce annually a large number of engines of this type in a series ranging from 3! H.P. to 260 H.P.; up to the end of 1920 this firm alone had built over 80,000 of these engines.

Many other important firms and companies are also engaged in this industry, among whom may be mentioned Messrs. Brotherhood, Browett-Lindley, The Campbell Co., Davey Paxman & Co., Fielding & Platt, Gardner, Grice, Hindley, The National Co., The Premier Co., Ruston & Hornsby, The Stock- port Co., Tangye, The Brit. Westinghouse Co., etc.

A typical combination of Suction Producer and gas engine is illustrated in fig. 6. Through an incandescent zone of anthracite or coke contained in the Producer or " Generator " a mixture of air and steam is drawn by the suction of the engine when at work. This air and steam in passing through the hot zone is decomposed, and issues from the generator as a very hot, smoky mixture consisting mainly of nitrogen, carbon monoxide, carbon dioxide, and hydrogen. A rough average composition by volume is as follows: nitrogen 55 %; carbon monoxide 22%; hydrogen 15%; carbon dioxide 6%; miscel- laneous hydrocarbons, free oxygen, etc., 2 %.

Such a mixture of gases is termed " Producer Gas " and has a (lower) calorific value of 125 to 130 B. Th. U. per cub. ft. ; about 200,- ooo cub. ft. are produced per ton of anthracite consumed.

The hot and smoky gas in the case illustrated passes first through a chamber fitted with a baffle plate, and water-sealed at the bottom ; here the grosser impurities are deposited ; thence it goes past a 2-way valve which permits its escape through a chimney into the atmos- phere when the engine is at rest ; when running, however, the gas is drawn by the engine suction through a large cylinder filled with small coke over which a spray of water is constantly played. This is termed the " coke scrubber," and here the gas is cooled and freed from dust and tarry impurities; thence finally it passes into a reser- voir, and so to the engine.

The illustration shows in section the normal type of horizontal 4- stroke cycle engine fitted with one or two massive fly-wheels which by their momentum maintain the required degree of uniformity of rotation of the crankshaft.

Vehicle and Marine Applications. In 1918-21 attention was again given to the problem of propelling motor road vehicles by small producer-gas engines, and a certain measure of success was obtained by Mr. D. J. Smith and others' experiments were in 1921 being continued. 2

Marine Producer-Gas Engines. In 1904 Herr Capitaine fitted a tug at Frankfort-on-Main with a 70 H.P. engine and an- thracite producer plant. In 1905 Messrs. Thornycroft fitted the launch " Emil Capitaine " with a 60 H.P. engine and producer, and, later, the barge " Duchess " with a similar 30 H.P. plant.

In 1908 Messrs. Beardmore fitted H.M.S. " Rattler, " 715 tons displacement, with an experimental 500 H.P. gas engine running at 120 revs, per minute on gas supplied by an anthracite producer. In 1910 the sailing boat " Castell san Nicolan " was fitted with an auxiliary 60 H.P. Gardner anthracite suction power plant.

The principal difficulty encountered with marine suction-gas plants was in obtaining efficient manoeuvring power; progress was made, though slowly, and it is of interest to record that the first producer-gas-engined ship crossed the Atlantic in 1919. The largest marine producer plant in 1921 was that of the American vessel " Wilhelmina," and comprised a 350 B.H.P. engine supplied by two suction gas producers.

The Dutch " Van Rennes " producer-gas engines, built in sizes up to a maximum of 200 H.P. have been fitted to a num- ber of small cargo-boats employed in coastal service; these engines are readily reversible, and it is claimed that their fuel consumption is, roundly, i Ib. of anthracite per H.P. hour.

A good class ocean-going cargo steamer may be taken as of about 8,000 tons dead weight, with steam engines of about 2,000 I. H.P. running at 65 revs, per minute and using iflb. of coal

2 Vide Proc. Inst. Auto. Engrs., xiv., 1919-20.